Image forming apparatuses, such as printers, facsimiles, copiers, and multifunction apparatuses, generally include a fixing device to fix toner images formed on sheets of recording media such as paper or overhead projector (OHP) films. Fixing devices typically include a heat source, a fixing member heated by the heat source, and a member disposed facing (or pressing against) the fixing member, forming a fixing nip therebetween. Such fixing devices fix the toner image on the sheet with heat and pressure while the sheet passes through the fixing nip.
If heat generated by the fixing device raises the temperature inside the image forming apparatus beyond a certain point, toner contained in a toner container inside the apparatus might be fused and coagulated, or components adjacent to the fixing device are affected adversely. For example, forced-exhaust means such as fans may be used to discharge hot air heated by the fixing device outside the apparatus.
However, it is possible that such forced-exhaust means generate noise, thus degrading ambient environmental conditions. Additionally, providing forced-exhaust means increases the size of the apparatus.
In view of the foregoing, natural convection may be employed in exhaust structures to discharge hot air released from the fixing device outside the apparatus without using any forced-exhaust means.
For example, JP-2007-298629-A proposes an exhaust structure designed to prevent hot air, heated by the fixing device and sheets transported through a post-fixing path immediately downstream from the fixing device, from flowing to the image forming unit. The structure includes a thermal shield that separates the fixing device and the post-fixing path from components susceptible to thermal effects, and an end of the thermal shield is connected to an exterior of the apparatus. Hot air is exhausted through an air channel formed between the thermal shield and the fixing device, and the air channel includes a horizontal portion. Although making a part of the air channel horizontal can increase design flexibility, velocity of the airflow decreases in the horizontal portion in natural convection methods.